This invention relates to impact drive tools, such as impact drive tools for driving nails or similar articles, and is more particularly directed to improvements in impact buffers for such impact drive tools.
Impact drive tools of the type under consideration herein include a percussive piston mounted to move in a cylinder. Means are provided for directing compressed air to one side of the piston, whereby the piston drives an impact ram, which in turn drives the nail or similar article into a workpiece. An impact buffer is provided to absorb impact energy at the end of an impact stroke.
In the use of impact drive tools of the above type, occasions arise where the impact buffer may be subjected to surplus striking energy, resulting from the use of excess striking pressures or from idle strikes of the percussive piston. Such surplus striking energy may result in the destruction of the impact drive tool, when the percussive piston is braked at the end of its impact stroke. For example, on occasion the nail supply feeding apparatus fails to properly load a nail into the drive tool, whereby the impact drive tool performs an "idle strike" and the entire striking energy of the impact tool must be absorbed by the impact buffer. In addition, in order to insure satisfactory driving of a nail in areas of greater strength of a workpiece, for example, an area containing knots, a surplus of impact energy must be provided. While such surplus energy enables the satisfactory driving of the nails in such areas, the surplus energy is not employed in the driving of the nail in places where the wood is less hard, and consequently the impact buffer must be capable of absorbing this surplus energy.
In the past, impact buffers provided in impact drive tools have been incapable of completely absorbing the striking energy in the event of idle strikes, since such impact buffers are designed to be completely compressed with a low striking energy of the percussive piston. The residue of the striking energy is thus transmitted to the casing of the drive tool. Considerable increases in pressure consequently occur which may result in fractures at the edges of the impact buffers, as well as in their complete destruction.
In the past it has been preferred to employ a polyurethane material, marketed under the trade name "VULKOLLAN" for the impact buffers. In order to absorb the striking energy without immediate damage to the buffer body, a VULKOLLAN quality with a hardness of at least 42 Shore D according to DIN 53 505 with a modulus of elasticity of at least 900 kgf/cm.sup.2 had to be used. Since drive tools of the above type are frequently portable tools having limited dimensions, a brake path of only approximately 4 to 5 millimeters was available to brake the percussive piston in known impact buffers. The high retarding forces resulted in rapid wear of the buffer body. Further, the occurrence of mass forces resulted in the reduction of life of the various individual components of the impact drive tool, such as the impact ram, casing, cylinder foot and magazine.